This invention relates to low profile magnetic components, and more particularly relates to such components including planar magnetic winding structures, such as inductors and transformers, in which the windings are composed of stacks of interconnected layers of conductor patterns.
The main use for such planar magnetic components is in electronic circuitry destined for use in a volume restricted space, ie, reduced height and/or reduced total volume.
Such structures consist of a stack of layers each containing part of the total winding structure, an insulating layer to prevent electrical contact between turns in adjacent layers, and a contacting structure that permits electrical contact between turns in adjacent layers. The winding structures are optimized with respect to winding losses, and usually are made by etching or stamping, and sometimes by folding. Contacts are usually made by soldering or using plated vias.
For example, the winding patterns may be formed by selectively etching a copper layer having a thickness of about 3 mils, from a PC board having a thickness of about 4 mils. The etched PC boards are then stacked to form the winding structure.
As such components are reduced in size to meet new miniaturized device requirements, the surface-to-volume ratio becomes smaller and the temperature due to heat dissipation quickly rises with the amount of dissipated heat. In present planar winding structures, such heat dissipation is hindered by the presence of voids between the layers and the windings of each layer, as well as by irregular outer surfaces of the structure, which prevents good thermal contact with surrounding structures. In addition, the layer-to-layer contacts become more difficult to achieve.
In DE 44 22 827 A1, to which U.S. Pat. No. 5,652,561 corresponds, the voids between winding layers of a planar magnetic winding structure are filled with glue, but the interconnections are achieved using vias. Such vias constitute a larger proportion of the total winding structure, which can contribute significantly to eddy current losses and other magnetic winding losses.
In U.S. Pat. No. 5,598,135, some of the interconnections between winding layers of a planar winding structure are achieved by brazing over connector portions of the windings which terminate in the outer surface of the stack. Such brazing is enabled by the use of a rigid ceramic composition as the insulating portion of the winding layers. However, vias must still be used to establish interconnections in the interior of the stack. Such a complex structure tends to be difficult and costly to manufacture.